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•    THE TRANSPORTATION OF GASES                        189
some solvent. The physical and chemical characteristics of each gas taken in the light of the limits of industrial conditions determine in what shape each gas is to be stored and used.
Gases having a very high liquefaction pressure, and not being soluble to a great extent in any other substance, are sold compressed; among these are oxygen, nitrogen, hydrogen, coal-gas, air, and most of the other so-called true gases.
Gases which liquefy within industrial limits of pressure and at atmospheric temperature are shipped as liquids, among which are chlorine, ammonia, blaugas, nitrous oxide, carbon dioxide, etc. Gases which are soluble to a large extent in some economical solvent, are sold in solution; among these are ammonia, hydrochloric acid and acetylene.
It is necessary to compress all of these gases whatever shape they are to be sold in. Gases are compressed by a combination of pressure and cooling. Jacket water is cheaper than power; hence, the best industrial compressors are of multi-stage construction, those for high pressures having as many as five stages with intercoolers between each stage.
Most gases when in a liquid state expand faster for an increase in temperature than do the steel containers in which they are to be shipped, and hence care must be taken to leave sufficient space for expansion above the liquid in the containers. When gases are to be handled either liquefied or absorbed, the containers holding them have to be filled by weight instead of by pressure. As noted above, an increase of pressure or decrease in volume of a saturated gas will not increase the gage reading, but will result in an accumulation of liquefied or dissolved gas. The pressure will remain the same, but the weight in the container will increase.
The gases which are sold in solution are absorbed in water for the most part. Acetylene might be sold either compressed or liquefied as the liquefaction pressure is approximately 700 Ib. at atmospheric temperature. Acetylene, however, acquires explosive properties when compressed in excess of some 20 Ib., and hence is not handled unabsorbed in either liquefied or compressed form. Acetylene is extremely soluble in and loses its explosive properties when absorbed in acetone, which is in turn absorbed in asbestos or some other porous non-inflammable material.1
In the handling of gases, the lubrication of the compressors is a question which requires consideration. The compressors handling the inert gases can be lubricated with oil. The compressors handling oxygen must not be lubricated with oil; but must use uncompounded graphite or a solution of soap in water, or glycerine in water. Chlorine in the presence of water has a very corrosive effect on iron; and water can-riot be used with chlorine in contact with iron. Chlorine has a destructive action upon oil. In the compression of this gas, concentrated sulphuric acid is used as a lubricant.
In handling compressed gas of any sort avoid any severe shocks to the drums; avoid any mixture within the drums or in any confined space of two gases that may react with one another; avoid any sudden temperature changes in the neighborhood of the drums; and if the gas is expanding through the gage-cock in the drum, keep it warm enough to avoid freezing the effluent gas. Avoid using any lubricants in the compressors that could, if volatilized, react with the gas being compressed. If the gas being compressed is combustible, avoid air leaks in the suction end. After all, a compressed gas is a high explosive and should be handled with the respect due the genus.
* Certain "garage experts " have been advising a mixture of acetylene and oxygen in a single cylinder as being more effective than the gases mixed in the burner. If this advice is followed to any considerable extent the coroners may anticipate some busy times. The mixture is itself likely to detonate, even were there no danger of the flame striking back through the burner.—EDITOR.